The present invention relates to wireless telecommunications. More specifically, the present invention relates to a technique for reducing unnecessary consumption of the air link resources and network capacity by reducing the size of transmitted messages.
The current third generation partnership project (3GPP) and internet engineering task force (IETF) session description protocol (SDP) protocol (RFC 2327) mandate that the proxy call state control functions (P-CSCF), the serving call state control functions (S-CSCFs) and the terminating end user (User Equipment UE) to examine the media contents of the session description protocol (SDP) text in the session initialization protocol (SIP) message.
FIG. 1 shows a simplified session initiation system. A user, UE-A 20, desires to initiate a media session with another user UE-B 40. In FIG. 1, UE-A 20 is shown as “roaming” in network A 22, not its home network. UE-A 20 sends a SIP invite message 441 to UE-B 40 via network A 22. The UE-A SIP invite 441 indicates all the media types that it can support. As shown in FIG. 1, the SIP invite 441 has a header, global information, and a list of the supported media types (media 1 to media 6). The supported media types include information for each media, such as the CODEC type, stream format, stream bit rate, and communication port number. Under the proposed system, there are no limits on the number of media types that a UE can include in the SIP invite message.
FIG. 2 is an example of a SIP invite message. The SIP invite message has a header, global information and supported media types for UE-A 20 for potential use in the proposed media session. The header includes various overhead information, such as the origin and destination of the SIP invite. The global information includes information common to all the proposed media types, such as the destination address and the proposed session identification (ID) number. The supported media types are listed. In this example, four media types are listed, two video (video media 1 and video media 2) and two audio (audio media 3 and audio media 4). Each proposed media session includes information regarding the media session, such as the port number, real time protocol (RTP) payload type and RTP format and clock rate port.
UE-A 20 sends the SIP invite to its current network, such as network A 22, in which it is currently located. UE-A may be “roaming,” as shown in FIG. 1 and communicating with a network, network A 22, or it may be in its home network, network B 30. The SIP invite 441 is examined by a P-CSCF 24 of its current network, such as network A 22, for routing to its destination, UE-B 40 via UE-A's home network, network B 30. The P-CSCF 24 examines the session description protocol (SDP) multimedia contents of the SIP invite 441 for validation and authorization. If the P-CSCF's network, network A 24, does not support any part of the media information, (such as the CODESs, bit rate or the type), it flags that portion of the media information by setting the port number to “0” and leaving the other contents of the media information untouched, as shown for media 5 and 6 for SIP invite 442.
FIG. 3 is an example of such a flagged SIP invite 44. To illustrate, the P-CSCF cannot support video media 1. As shown in FIG. 3, the port number is set to “0” so that UE-B 40 realized that video media 1 cannot be selected for the media session.
The network A P-CSCF 24 forwards the modified SIP invite 442 to the network B S-CSCF 26 for further handling, routing and validation. If UE-A 20 is in the home network, both the P-CSCF and S-CSCF function are performed by the home network 30. The network B S-CSCF 26 examines the SIP invite 442 including the media information. Media types not supported by UE-A's service license agreement (SLA) are flagged. If UE-A 20 is in its home network, the flagging process is only performed by the S-CSCF 26, not by the P-CSCF 24. The S-CSCF 26 forwards the SIP invite 443 to UE-B's home network, network C36, using intorgating-CSCFS (I-CSCF) 28, 32.
The network C S-CSCF 34 similarly examines the SIP invite 443 for media types not available under UE-B's SLA. The not available media types are flagged, as illustrated for media 1 and of SIP 444. If UE-B 40 is not in its home network, as shown, the SIP invite 444 is forwarded to the P-CSCF 38 of the network, network D 42, where UE-B 40 is currently located, or “roaming.” If UE-B 40 is in its home network, the SIP invite 444 is forwarded to the P-CSCF 38 of the home network.
The P-CSCF 38 flags the media types not supported by the network, network D. No additional flagged media types are shown in SIP invite 445. If the UE-B is in its home network, the flagging is only performed by the S-CSCF 34. The P-CSCF 38 sends the SIP invite 445 to UE-B 40. UE-B 40 examines the media information of the SIP invite 445 and determines whether it is capable of using any of the unflagged media types. If it can not use any of the unflagged media types or there are not any remaining unflagged media types, UE-B 40 sends UE-A 20 a session description protocol message (SPM) 46 with all media types flagged. If it can use the unflagged media types, UE-B 40 selects one or more of the available media types for the session. The selected media types unflagged and the flagged media types are returned to UE-A 20 in the SPM 44.
As shown in FIGS. 2 and 3, the SIP invite message 44 is large and, accordingly, consumes valuable air interface and wireless network resources. This resource consumption either degrades the network performance or reduces the maximum number of users serviced by the networks.
Accordingly, it is desirable to have alternate approaches for media session initiation.